Increasing demand for high speed operation of central processing units of electronic computers causes need for high speed processing output devices, i.e. high speed printing apparatus.
In one of the typical types of printing apparatus, there is a printing system in which ink is supplied to the nozzle under a slight pressure so that the ink forms as a hemispherical shape at the tip of the nozzle, and the ink is drawn in droplet form by applying an electric field between an accelerating electrode positioned a few milimeters ahead of the nozzle and the nozzle, and droplets of ink are moved toward the surface of the recording paper by applying a high electric field between the nozzle and platen. The droplets of ink are electrostatically deflected in both directions (right and left) to print characters or symbols on the surface of the recording paper.
Another typical printing apparatus is one in which ions produced between electrodes carrying high voltage are passed through mists of ink and the particles of ink are selectively adhered to the surface of the recording paper to obtain printing. The present invention relates to this type of printing apparatus.
The printing system will be described in detail. The ionization of the air is carried out by utilizing corona discharge. Application of a few thousand volts to a very thin conductor cause a corona discharge to occur, and molecules such as oxygen, nitrogen or the like in the air surrounding this conductor are ionized. The ions produced around this conductor are attracted to the platen side by the electric field existing between the back of the recording paper and the platen.
The ink of this system are agitated by supersonic waves, changed into a mist having drops with diameters of 5 to 20 .mu. and suspended in the air. This mist is fed between the platen and a source of corona discharge by pneumatic pressure in the same direction as that of the feeding paper and at approximately the same speed as that of the feeding paper. Thus, said ions are passed into the mist of ink, adhered around the mist, moved in the combined directions of electrostatic force and the force of the flow of the mist, and adher recording paper positioned between the platens.
The general configuration of the type of apparatus used is shown in the block diagram of FIG. 1, and comprises two parts, a main body 11 and a control part 12. The main body 11 has a paper feeding device 13, a printing part 14, a mist generating part 15, an ink circulating device 16 and a mist treatment device 17, and the control part 12 has a control circuit 18 and a driving circuit 19 for the mist generating device.
Thus, in the above-mentioned type of high-speed printing device, ink mists being fed in front of the recording paper are recovered and fed to the condensor, therein separated to the ink solution and the air, and the air is discharged outside the apparatus. However, this air has a smell produced by the solvent of the ink and cause the operator discomfort.
It is an object of the present invention to provide a system in which the separated air is again fed to the printing part and circulated, and is prevented from being leaked outside the apparatus, as little as possible.